A lithium-ion secondary battery having a negative electrode layer formed with a material capable of intercalating/deintercalating lithium-ion is able to suppress deposition of dendrite more effectively compared to a lithium-ion secondary battery having a negative electrode layer formed with metallic lithium. Therefore, the former lithium-ion secondary battery has the advantage of providing an increased capacity and energy density while improving the safety by preventing electrical short circuit.
While there is demand for a further increase in capacity of the lithium-ion battery, the flatness of discharge voltage and a high output of a lithium-ion secondary battery have been also in demand in recent years. Under such a circumstance, various attempts have been made. Examples of the attempts include: to increase the capacity of a positive electrode metallic lithium oxide composite and a negative electrode material themselves, which are electro chemical reactants; to increase the planer dimension of an electrode at the designing stage, and to increase the amount of reactant by thinning a separator. (Refer to the below patent documents 1 to 5)
[Patent Bibliography 1]
    Japanese Unexamined Patent Publication No. 8-213014[Patent Bibliography 2]    Japanese Unexamined Patent Publication No. 2000-113907[Patent Bibliography 3]    Japanese Unexamined Patent Publication No. 2001-210325[Patent Bibliography 4]    Japanese Unexamined Patent Publication No. 2004-192896[Patent Bibliography 5]    Japanese Unexamined Patent Publication No. 2005-11688